This invention is a continuation to and a refinement over applicant's earlier patent efforts in this area as generally titled "Air Ride Boat Hull". As in all of the others, it involves the introduction of pressurized gas in one or more recesses under a boat hull to augment hull lift and thereby improve hull load carrying capability, efficiency, ride quality and speed. Of particular focus in this continuation is the development of diverging sidehull keels which contribute to ride quality and reduce gas leakage forward without sacrificing the other aspects of the invention as taught by other disclosures made by the inventor.
The recess is bounded by bow shaped members at its forward and aft portions, and optionallv. therebetween, and by stabilizing, planing, catamaran-like sidehulls, whose keels diverge over at least part of their length. The combination of these elements gives the aforementioned performance advantages over conventional hulls while offering operation, costs, and aesthetic advantages over other pressurized air hull craft. The invention described herein handles much like conventional hulls with the pressurized gas supply either "on" or "off" costs the same or only slightly more to manufacture and maintain than conventional hulls and offers generally the payload space, while maintaining essentially the same above-water aesthetics as conventional hulls.
Tests have shown that the secondary bow-shaped members, while in some cases adding slightly to overall vehicle drag, provide excellent ride and tracking characteristics and improved gas retention means since the aft bow-shaped member, and optionally, any intermediate bow shaped member if so designed, actually rides in the water like a small boat bow section.
The idea of introducing air or other gases at ambient or higher pressures under boat hulls is not new in basic concept and patents have been issued on several approaches. Only a few of the more sophisticated developments have met with any commercial success. However, due to their complex structural requirements and elaborate flexible seals they remain too expensive or impractical for general marine applications. The only example of the latter that has any applicability here is the Surface Effect Ship (SES) as it is known in the United States. The SES is an outgrowth of the success of the Ground Effect Machine (GEM) as first made workable by Christopher Cockerell over two decades ago in England. The GEM is totally supported by an air cushion and has flexible seals around its full periphery. As such it is truly amphibious and has little relationship to this invention.
The SES is a substantially rectangular shaped platform with widely spaced, deep vertical side members that extend downward from the main platform. The side members are connected fore and aft by full span flexible seals or flaps, and the deep wave clearing chamber thus defined is pressurized with air. The SES requires substantially less chamber air flow and therefore less fan power than the GEM but is limited to a marine environment. The SES is capable of very high speeds, offers a smoother ride than conventional craft due to proportionally thin side members and the flexibility of the seals, and is significantly more efficient than conventional craft due to the minimum wetted area. The SES offers much potential as a military and commercial craft notwithstanding its high initial cost, deep static draft due to the vertical side members, inherently high stress structure and high maintenance flexible seals. The U.S. Navy has extensively tested SES prototypes including two 100 ton craft and is presently working on designs of SES's of 3000 tons and more. Also, recent commercial SES ventures appear promising but are reported to be several times as expensive as equivalent size conventional hulls.
Some patents related to the SES and some of its variations include one that utilizes large flap-like seals, Ford, U.S. Pat. No. 3,146,752. More appropriate to current SES technology are Beardsley, U.S. Pat. No. 3,140,687, and Mantle, et al., U.S. Pat. No. 3,476,069. These latter examples use the more flexible fabric type seals. The most extreme variation appears to be Gunther, U.S. Pat. No. 3,473,503, who describes an attempt at an amphibious SES type craft that has surface-contacting, flexible, vertical, side members as well. In any case, all of the aforementioned craft differ substantially from the invention in that they use flexible or flap-like seal members fore and aft (as opposed to the substantially rigid structure of this invention), devote much usable hull space to the air chamber to allow wave clearance between the side members, and deviate widely in appearance from conventional marine craft. They also have been reported to suffer from instability problems, particularly in small size craft.
Crowley, U.S. Pat. No. 3,742,888, attempts to resolve admitted instability problems by incorporating discrete pressurized air chambers around the periphery of the hull. His theory is that as one of the high pressure peripheral chambers submerges, its pressure increases further while its opposite member loses pressure thereby causing a hull righting moment. In any case, his is an ungainly and assuredly rough riding craft that compromises the majority of useful hull space. It is primarily concerned with resolving particular instability problems related to the design which offers little resemblance to conventional marine craft and requires the high pressure peripheral chambers for any degree of stability. Continuous pressurization with Crowley's design is essential, and deep draft at rest results.
One more approach is that of Wukowitz, U.S. Pat. No. 3,726,246, who has a ram air inlet in the forward end of the hull that supplies air to a divergent channel under the hull. It will be noted that Wukowitz does not teach that catamaran sidehulls extend downwardly from the main hull as in the principal embodiment of this invention. His divergent channel is actually a chamber inset into the hull absent any sidehulls, which divergent channel converts the dynamic energy (pressure) of the air to static pressure, according to Bernoulli's Theorem, and thus increases lifting pressure. In his application of Bernoulli's principle, Wukowitz does not and cannot teach means to seal the aft end of his channel. As a result, little lift would be provided even if the forward ram air inlet were to be supplemented by artificial means. The lack of means to restrain the air at the aft end of the channel makes the approach of Wukowitz impractical to meet the accomplishments of the present invention.
Another approach that deviates far afield from more conventional aspects of marine design is given by Szptyman, U.S. Pat. No. 3,702,598, who offers a tunnel hull with an aerodynamic lifting surface that receives ram air from a forward opening in the air chamber that can be supplemented by artificial means. This craft can only realize reasonable chamber lift values at very high speeds where ram air pressure is sufficient to maintain high chamber pressures. Also, Szptyman's invention bears little aesthetic resemblance to conventional marine craft.
There have also been attempts to inject air under hulls of more or less conventional form. Patents that exist in this area are Glass, U.S. Pat. No. 3,547,064, and Von Heidenstam, U.S. Pat. No. 3,331,347. There is a major difference between their patents and this invention in that they place an air layer under the hull that cannot be maintained at any lift-providing pressure since there is insufficient structure on the sides of the layer to do so.
There are also conventional hull forms that offer underwater cavities or tunnels of various types. Some of them include Grayson, et al., U.S. Pat. No. 1,835,564, Stuart, U.S. Pat. No. 3,937,173, Walker, U.S. Pat. No. 3,477,400, Higgins, U.S. Pat. No. 2,234,899, and Sartori, U.S. Pat. No. 2,231,296. None of these patents show a pressurized restrained air or gas layer under the hull even though several show cavities in the hull of one type or another. They must be considered variations of more or less standard hull forms without benefit of a pressurized gas lifting force that is confined by structure, which is a primary object of this invention.
As noted above, the present invention is a derivation from applicant's other inventive efforts with improved performance marine surface vessels that are in part supported by a pressurized gas layer structurally trapped and restrained beneath the hull. Actual test results utilizing a forty-two foot craft built in this manner show the viability of this concept. The test vehicle, a forty-two by fifteen foot welded aluminum craft has achieved in actual practice substantial efficiency improvements as compared to conventional hull forms. Based on the test results, it can be said that, in moderate and heavy load carrying applications, conventional hulls will generally require from fifty to one hundred percent more power at planing speeds than a hull with concepts embodied in applicant's prior inventions in this area. Additionally, the air ride invention normally realizes at least a thirty percent speed advantage. These performance advantages are similar to those experienced by the complex and vastly more expensive SES described above.
Since the bottom line on any commercial venture is cost, it should be considered that a one hundred ten foot off-shore oil industry crew and supply boat built to a conventional design would cost about 1.2 million dollars while a one hundred ten foot SES is in the four million dollar cost range. A one hundred ten foot air ride vessel built according to the present invention would cost thirty percent more than the conventional hull or about 1.6 million dollars. The air ride's higher speed and greater payload capability will pay back any of the cost difference between it and the conventional hull normally within the first year of operation. The difference between the 4 million dollar cost of a one hundred ten foot SES and the 1.6 million dollars for a one hundred ten foot vessel built according to the present invention is enough to cover fixed operating expenses less depreciation of the present invention for over fifteen years.